1. Field of the Invention
This invention generally relates to electrochemical batteries and, more particularly, to a method for the plating of an alkali or alkane earth metal over the anode of a transition metal cyanometallate (TMCM) cathode battery.
2. Description of the Related Art
Energy storage for renewable but variable solar and wind power has instigated an urgent demand for rechargeable batteries. Although rechargeable lithium-ion batteries are currently dominating this application, the goal of meeting a cost target of less than $100 per kilowatt hour (/kWh) is proving to be formidable. Sodium-ion batteries with insertion-compound cathodes analogous to the cathodes of lithium-ion batteries offer a higher energy density than aqueous batteries and a lower cost than lithium-ion batteries [1]. The layered oxides and framework structures containing (XO4)n− polyanions [2] that have been studied as cathodes for Na-ion batteries show a limited capacity that is further reduced in a cell that must be fabricated in a discharged state with an anode devoid of Na atoms. In addition, their high-temperature synthesis is a process of high energy consumption. On the other hand, Prussian-blue analogues (PBAs) with the general chemical formula AxMa[Mb(CN)n]y.zH2O are framework structures synthesized at low temperature that support a reversible extraction of two Na/formula units (fu) at high rates, with a good cycle life.
Prussian-blue analogues, or transition metal cyanometallate (TMCM), have been investigated as the cathode materials for rechargeable lithium-ion batteries [3,4], sodium-ion batteries [5, 6], and potassium-ion batteries [7]. With an aqueous electrolyte containing alkali-ions or ammonium-ions, copper and nickel hexacyanoferrates ((Cu,Ni)-HCFs) exhibited a very good cycling life, where 83% capacity was retained after 40,000 cycles at a charge/discharge current of 17C [9-10], where 1C is the current, per gram, required to fully charge or discharge a battery in one hour. However, the materials demonstrated low capacities and energy densities because (1) only one sodium-ion can be inserted/extracted into/from per Cu-HCF or Ni-HCF formula and (2) these transition metal (TM)-HCFs electrodes must be operated below 1.23 V due to water electrochemical window. To correct for these shortcomings, manganese hexacyanoferrate (Mn-HCF) and iron hexacyanoferrate (Fe-HCF) were used as cathode materials in a non-aqueous electrolyte [11, 12]. Assembled with a sodium-metal anode, Mn-HCF and Fe-HCF electrodes were cycled between 2.0V and 4.2 V and delivered capacities of about 110 milliamp hours per gram (mAh/g).
To improve the capacity even further, a sodium-ion battery with a non-sodium anode would be useful. Currently, non-sodium metal anodes can be put into three categories: carbonaceous materials, metals/metal chalcogenides (oxides and sulfides), and organic chemicals. However, there are unique challenges that must be overcome for each type of material, for example, slow sodiation kinetics for hard carbon, pulverization for alloys, and dissolution for organics.
It would be advantageous if a new anode strategy could be adopted in order to develop practical sodium-ion batteries.    [1]Yabuuchi, N.; Kajiyama, M.; Iwatate, J.; Nishikawa, H.; Hitomi, S.; Okuyama, R.; Usui, R.; Yamada, Y.; Komaba, S. Nat. Mater. 2012, 11, 512.    [2]Palomares, V.; Casas-Cabanas, M.; Castillo-Martinez, E.; Han, M. H.; Rojo, T. Energy Environ. Sci. 2013, 6, 2312.    [3]V. D. Neff, Some performance characteristics of a Prussian Blue battery, Journal of Electrochemical Society, 132 (1985) 1382-1384.    [4]N. Imanishi, T. Morikawa, J. Kondo, Y. Takeda, O. Yamamoto, N. Kinugasa, T. Yamagishi, Lithium intercalation behavior into iron cyanide complex as positive electrode of lithium secondary battery, Journal of Power Sources, 79 (1999) 215-219.    [5]Y. Lu, L. Wang, J. Cheng, J. B. Goodenough, Prussian blue: a new framework for sodium batteries, Chemistry Communication, 48(2012)6544-6546.    [6]L. Wang, Y. Lu, J. Liu, M. Xu, J. Cheng, D. Zhang, J. B. Goodenough, A superior low-cost cathode for a Na-ion battery, Angew. Chem. Int. Ed., 52(2013)1964-1967.    [7]A. Eftekhari, Potassium secondary cell based on Prussian blue cathode, J. Power Sources, 126 (2004) 221-228.    [8]C. D. Wessells, R. A. Huggins, Y. Cui, Copper hexacyanoferrate battery electrodes with long cycle life and high power, Nature Communication, 2(2011) 550.    [9]C. D. Wessells, S. V. Peddada, R. A. Huggins, Y. Cui, Nickel hexacyanoferrate nanoparticle electrodes for aqueous sodium and potassium ion batteries. Nano Letters, 11(2011) 5421-5425.    [10] C. D. Wessells, S. V. Peddada, M. T. McDowell, R. A. Huggins, Y. Cui, The effect of insertion species on nanostructured open framework hexacyanoferrate battery electrode, J. Electrochem. Soc., 159(2012) A98-A103.    [11] T. Matsuda, M. Takachi, Y. Moritomo, A sodium manganese ferrocyanide thin film for Na-ion batteries, Chemical Communications, DOI: 10.1039/C3CC38839E.    [12]S.-H. Yu, M. Shokouhimehr, T. Hyeon, Y.-E. Sung, Iron hexacyanoferrate nanoparticles as cathode materials for lithium and sodium rechargeable batteries, ECS Electrochemistry Letters, 2(2013)A39-A41.